The present disclosure relates to use of a polymer as a processing additive in a polyvinyl chloride polymer composition.
The present invention concerns polyvinyl chloride and polyvinyl chloride processing. More particularly, but not exclusively, this invention relates to use of a polymer as a processing aid in a polyvinyl chloride polymer composition. The invention also concerns a method of processing a polyvinyl chloride polymer composition, a composition for synthesising a polyvinyl chloride polymer, a processing aid, a method of making a polyvinyl chloride composition and a polyvinyl chloride polymer composition.
Polyvinyl chloride (often known as PVC) is well known to those skilled in the art. It is a versatile and relatively inexpensive polymer to which may be added many additives in order to obtain the desired properties for processing and for the polymer once processed. Melt processing additives are one type of additive which is well known to those skilled in the art. These melt additives are typically in the form dry powders or polymers. Powders are typically added to the PVC polymer and dry blended using a blender. This requires a separate operation, furthermore it requires additional energy and it has the potential to create dust and high shear blending may impart unwanted thermal history into the grains of polyvinyl chloride polymer. Furthermore, dry powder additives require that an emulsion polymer is first produced in aqueous solution, and then it must be coagulated (and comminuted) or spray dried. It is well known that spray drying of emulsion polymers is an energy intensive process, and further complicated by the desire to produce agglomerated versions to prevent dust evolution and dust explosions. Indeed, in the case of acrylic and butadiene based emulsions the spray drying must be carried out under “low oxygen” or inert atmosphere conditions in order to mitigate against dust explosions.
Certain polymers may be used as a melt processing aid. The predominant chemistry used for melt processing aids is based upon copolymers of methyl (meth)acrylate and a low level (typically 10-20 wt %) of ethyl acrylate. Typical usage levels for processing aids are 0-2 phr (parts per hundred of PVC polymer), but can increase to 5-8 phr in rigid foam extrusion compounds. Such acrylic processing aids typically lead to an unwanted increase in viscosity, as shown by an increased fusion torque using a torque rheometer.
The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved processing aid, method of processing a polyvinyl chloride polymer composition and/or a polyvinyl chloride polymer composition.